The subject matter of the present invention relates generally to wooden structural support members such as wooden joists, trusses or I-beams. The wooden joists are formed with two flange members having tapered grooves in their facing surfaces and joined together by a closed web including wooden web members having tapered outer edges which are glued into such grooves. Such a wooden joist can be employed as a structural support member in a building, a bridge or other structure.
Previously it has been suggested in U.S. Pat. No. 3,490,188 of Troutner issued Jan. 20, 1970 to provide a wooden joist or truss of the above-described closed web type which employs two tapered edges formed by compression of the edges on the opposite sides of the web member beyond their elastic limit. The compressed tapered edges absorb water or other solvent in the glue to cause swelling of such edges which results in a wedging pressure between the tapered edges of the web and the chord members. While, for most purposes this structure has proved satisfactory, the wood fibers are damaged during compression to form the tapered edges which weakens the joint. However, such compressed joist cannot be employed when using oriented strand board for the web member since compression of such board beyond its elastic limit breaks the edge of the board. Also only a small amount of water or solvent is absorbed in the compressed oriented strand board, so there is no appreciable expansion.
In addition, it has been proposed in U.S. Pat. No. 4,336,678 of Peters issued June 29, 1982 to provide an I-beam truss structure or joist of the above-mentioned closed web type in which the web member is made of plywood whose tapered edges are formed by compression of such plywood which may vary in thickness, + or -1/16 inch. Glue vents are formed by pressing the compressed tapered edges of the web member in order to further compress such edges at spaced positions on the edges to form glue vents. Such compression is apparently beyond the elastic limit of the wood material which weakens the web member. Also, because of the thickness variations of standard commercial plywood, the web is of non-uniform thickness and density which further reduces the strength of the joint. The glue vents are preferably formed as scallops by means of eccentric compression rollers so that the depth of the glue vent varies along its length. As a result, such compressed glue vents reduce in depth to a minimum adjacent the top of the groove and, therefore are not sufficient in transmitting the flow of glue out of the grooves in the flange members. Also the glue is provided in the bottom of the grooves and does not spread uniformly over the sides of the groove and the tapered edges.
The wooden truss of the present invention employs web members whose tapered outer edges are formed by cutting, not compression, to provide stronger web members. Also the plurality of vent slots spaced longitudinally along such edges are formed by cutting so that such vent slots are of substantially uniform depth along the entire length of the slot. The result is a more uniform distribution of glue on the sides of the grooves of the flange members and over the surface of the tapered edges of the web member. This provides a much stronger bond between the web member and the flange members which in turn provides a stronger joist apparatus. In addition, the method of manufacture of a joist in accordance with the present invention enables oriented strand board or plywood of cut accurate dimensions to be employed for the web member which insures that a strong glue bond is formed between the web member and the flange member.